1. Field of the Invention
This invention relates in general to the field of microelectronics, and more particularly to a an apparatus and method for overriding a tamper protection mechanism for a programmable fuse array within an integrated circuit.
2. Description of the Related Art
Many present day integrated circuits employ metal or polymer fuses disposed on their die to enable and disable functional elements and extended features. Typically these fuses are blown at the factory during fabrication to yield a specific version of a device. For example, a common design for a microprocessor may include a cryptography unit or other security features which are placed on the die, but which are enabled for operation by blowing certain fuses. Accordingly, economies of scale can be achieved during production of the microprocessor while still providing the manufacturer with the ability to easily produce variants of the microprocessor with a range of capabilities and price points.
In more recent years, however, designers have been providing the capability to not only enable/disable these features during fabrication, but also to enable/disable selected features in the field, by providing the mechanisms on chip to allow certain fuses to be blown post production. In most configurations, this field programmability of features is accomplished through sending specific commands and data through the well-known Joint Test Action Group (JTAG) interface/protocol that is present on virtually all microprocessors, cell phone chips, and the like. By sending the proper commands and data, and by perhaps manipulating voltages on specified package pins at prescribed intervals, on-die fuses can be selected and blown, thus enabling or disabling the selected features in the field.
As more and more features are provided that allow for field programmability as described above, the present inventors have noted that the opportunity and motivation exist for an unauthorized user to reconfigure a fielded integrated circuit without the permission of the device manufacturer.
Consequently, what is needed is an apparatus and method for precluding the unauthorized programming of fuses in the field to enable or disable features of a device.
In addition, what is needed is a mechanism for determining if an unauthorized user is attempting to tamper with a device's feature programmability, and for precluding such programming.
Moreover, what is needed is a technique that allows a manufacturer to temporarily re-enable field programming of a device to allow for authorized enablement and disablement of field programmable features.